[NFC] Add error checking for InlinedAts.

The DroppedVariableStats::calculateDroppedStatsAndPrint should check if
it's InlinedAts stack contains the the function name that is being
accessed to make sure that a pass did not create a new function
declaration which may then lead to a crash. For example, in hot-cold
splitting, the Module before the pass will not contain the newly created
cold function and can cause a crash when trying to access the InlinedAts
stack with the function name of the newly created cold function.

Author: rastogishubham

llvm/include/llvm/Passes/DroppedVariableStats.h

@@ -96,6 +96,8 @@ class DroppedVariableStats {
     DenseSet<VarID> &DebugVariablesBeforeSet =
         DbgVariables.DebugVariablesBefore;
     DenseSet<VarID> &DebugVariablesAfterSet = DbgVariables.DebugVariablesAfter;
+    if (InlinedAts.back().find(FuncName) == InlinedAts.back().end())
+      return;
     DenseMap<VarID, DILocation *> &InlinedAtsMap = InlinedAts.back()[FuncName];
     // Find an Instruction that shares the same scope as the dropped #dbg_value
     // or has a scope that is the child of the scope of the #dbg_value, and has